AU2023333610A1 - Apparatus for producing organic hydride and method for producing organic hydride - Google Patents

Abstract

This apparatus 2 for producing an organic hydride is provided with: a cathode electrode 10 which generates an organic hydride and hydroxide ions from an object to be hydrogenated and water; an anode electrode 12 which generates oxygen by oxidizing the hydroxide ions; and an electrolyte membrane 14 which is composed of an anion exchange membrane and is arranged between the cathode electrode 10 and the anode electrode 12 so as to transfer the hydroxide ions from the cathode electrode 10 side to the anode electrode 12 side.

Description

DESCRIPTION TITLE OF INVENTION: APPARATUS FOR PRODUCING ORGANIC HYDRIDE AND METHOD FOR PRODUCING ORGANIC HYDRIDE TECHNICAL FIELD

[0001] The present invention relates to an apparatus for

producing an organic hydride and a method for producing an

organic hydride.

BACKGROUND ART

[0002] In recent years, in order to suppress the carbon

dioxide emission amount in the energy generation process,

renewable energy is expected to be used, which is obtained by

solar light, wind power, hydraulic power, geothermal power

generation, and the like. As an example, a system for

generating hydrogen by performing water electrolysis using

power derived from renewable energy has been devised. In

addition, an organic hydride system has attracted attention

as an energy carrier for large-scale transportation and

storage of hydrogen derived from renewable energy.

[0003] Regarding the technology for producing an organic

hydride, there has been known an apparatus for producing an

organic hydride having an anode electrode that generates

protons from water, a cathode electrode that hydrogenates an

organic compound having an unsaturated bond (a substance to

be hydrogenated), and an electrolyte membrane that separates

the anode electrode and the cathode electrode (see, for

example, Patent Literature 1). In this apparatus for producing an organic hydride, protons are generated by oxidation of water at the anode electrode, these protons then move to the cathode electrode side via the electrolyte membrane, and a substance to be hydrogenated is hydrogenated by the protons at the cathode electrode, thereby producing an organic hydride.

RELATED-ART LITERATURE PATENT LITERATURE

[0004] Patent Literature 1: WO 2012/091128

SUMMARY OF INVENTION TECHNICAL PROBLEM

[0005] In the above-described apparatus for producing an

organic hydride, the protons bind with water in the anode

chamber so as to become oxonium ions and then move to the

cathode electrode side via the electrolyte membrane. When

three elements: oxonium ions, a substance to be hydrogenated;

and electrons, are present in the reaction field of the

cathode electrode, the protons are consumed from the oxonium

ions, and a hydrogenation reaction of the substance to be

hydrogenated occurs. As a result of this, water is produced.

Further, as the ions move, the water solvated with the

protons also moves at the same time. Hereinafter, water that

moves through the electrolyte membrane with the movement of

ions is collectively referred to as "electroosmotic water."

If electroosmotic water accumulates on the cathode electrode

side, it may hinder the hydrogenation of the substance to be hydrogenated or may require a lot of work to separate the water from the organic hydride. As a result, the production efficiency of the organic hydride can be reduced.

[00061 The present invention has been made in view of

such a situation, and an object thereof is to provide a

technique for improving the production efficiency of organic

hydrides.

SOLUTION TO PROBLEM

[0007] One embodiment of the present invention relates

to an apparatus for producing an organic hydride. This

apparatus for producing an organic hydride includes: a

cathode electrode that generates an organic hydride and

hydroxide ions from a substance to be hydrogenated and water;

an anode electrode that generates oxygen by oxidizing the

hydroxide ions; and an electrolyte membrane that is composed

of an anion exchange membrane and is arranged between the

cathode electrode and the anode electrode so as to transfer

the hydroxide ions from the cathode electrode side to the

anode electrode side.

[00081 Another embodiment of the present invention

relates to a method for producing an organic hydride in which

the apparatus for producing an organic hydride according to

the above embodiment is used. The method for producing an

organic hydride includes: producing an organic hydride and

hydroxide ions from the substance to be hydrogenated and

water at the cathode electrode; moving the hydroxide ions to the anode electrode via the electrolyte membrane; and producing oxygen by oxidizing the hydroxide ions at the anode electrode.

[00091 Optional combinations of the aforementioned

constituting elements, and implementations of the present

disclosure in the form of methods, apparatuses, and systems

may also be practiced as additional modes of the present

disclosure.

ADVANTAGEOUS EFFECTS OF INVENTION

[0010] According to the present invention, it is

possible to improve the production efficiency of organic

hydrides.

BRIEF DESCRIPTION OF DRAWINGS

[0011] [Fig. 1] Fig. 1 is a schematic diagram of an

organic hydride production system according to an embodiment.

[Fig. 2] Fig. 2 is a diagram showing evaluation results

of the Faraday efficiency and evaluation results of water

mixed into a catholyte in each of exemplary embodiments and

comparative examples.

DESCRIPTION OF EMBODIMENTS

[0012] Hereinafter, the present invention will be

described based on preferred embodiments with reference to

the drawings. The embodiments do not limit the technical

scope of the present invention and are shown for illustrative

purposes, and not all the features described in the

embodiments and combinations thereof are necessarily essential to the invention. Therefore, regarding the details of the embodiments, many design modifications such as change, addition, deletion, etc., of the constituent elements may be made without departing from the spirit of the invention defined in the claims. New embodiments resulting from added design change will provide the advantages of the embodiments and variations that are combined. In the embodiments, the details for which such design change is possible are emphasized with the notations "according to the embodiment,"

"in the embodiment," etc. However, design change is also

allowed for those without such notations. Optional

combinations of the constituting elements described in the

embodiments are also valid as embodiments of the present

invention. The same or equivalent constituting elements,

members, and processes illustrated in each drawing shall be

denoted by the same reference numerals, and duplicative

explanations will be omitted appropriately. The scales and

shapes of parts shown in each figure are set for the sake of

convenience in order to facilitate the explanation and shall

not be interpreted in a limited manner unless otherwise

mentioned. Terms like "first," "second," etc., used in the

specification and claims do not indicate an order or

importance by any means and are used to distinguish a certain

feature from the others. Some of the components in each

figure may be omitted if they are not important for

explanation.

[0013] Fig. 1 is a schematic diagram of an organic

hydride production system 1 according to an embodiment. The

organic hydride production system 1 as an example includes an

apparatus 2 for producing an organic hydride, a catholyte

supply device 4, and an anolyte supply device 6. Although

only one apparatus 2 for producing an organic hydride is

shown in Fig. 1, the organic hydride production system 1 may

include a plurality of apparatuses 2 for producing an organic

hydride. In this case, the respective apparatuses 2 for

producing an organic hydride are stacked in the same

direction such that the cathode electrode 10 and the anode

electrode 12 are arranged in the same direction, and are

electrically connected in series. Note that the apparatuses

2 for producing an organic hydride may be connected in

parallel, or may be a combination of series connection and

parallel connection.

[0014] The apparatus 2 for producing an organic hydride

is an electrolysis cell for generating an organic hydride by

hydrogenating a substance to be hydrogenated, which is a

dehydrogenated product of the organic hydride, by an

electrochemical reduction reaction. The apparatus 2 for

producing an organic hydride includes a membrane electrode

assembly 8, a pair of plate members 16a and 16b, and a pair

of gaskets 18a and 18b. The membrane electrode assembly 8

includes a cathode electrode 10 (cathode), an anode electrode

12 (anode), and an electrolyte membrane 14. In the present embodiment, an explanation will be given using the membrane electrode assembly 8 as an example, and the apparatus 2 for producing an organic hydride may have a so-called zero-gap electrode structure in which an electrode having an anode catalyst applied to a hard support substrate is in physical contact with the electrolyte membrane.

[0015] The cathode electrode 10 produces an organic

hydride and hydroxide ions from the substance to be

hydrogenated and water. The cathode electrode 10 contains

precious metals such as platinum (Pt), ruthenium (Ru), and

palladium (Pd) and base metals such as nickel (Ni) as a

cathode catalyst for hydrogenating the substance to be

hydrogenated with water. It is preferable that the cathode

electrode 10 also contains a porous catalyst support that

supports the cathode catalyst. The catalyst support includes

an electron-conductive material such as porous carbon, a

porous metal, or a porous metal oxide.

[0016] Furthermore, the cathode catalyst is coated with

an anion-exchange ionomer. For example, the catalyst support

in the state of supporting the cathode catalyst is coated

with an ionomer. Examples of the ionomer include polymers

such as Fumion (registered trademark). It is preferable that

the cathode catalyst is partially coated with the ionomer.

As a result, it is possible to efficiently supply three

elements (the substance to be hydrogenated, water, and an

electron) necessary for an electrochemical reaction in the cathode electrode 10 to the reaction field.

[0017] As an example, the cathode electrode 10 has a

catalyst layer 10a and a diffusion layer 10b. The catalyst

layer 10a is disposed closer to the electrolyte membrane 14

than the diffusion layer 10b. The catalyst layer 10a

contains the cathode catalyst, the catalyst support, and the

ionomer described above. The diffusion layer 10b is in

contact with a main surface of the catalyst layer 10a on a

side opposite to the electrolyte membrane 14. The diffusion

layer 10b uniformly diffuses the substance to be hydrogenated

supplied from the outside into the catalyst layer 10a. The

organic hydride generated in the catalyst layer 10a is

discharged to the outside of the cathode electrode 10 through

the diffusion layer 10b. The diffusion layer 10b includes a

conductive material such as carbon or a metal. In addition,

the diffusion layer 10b is a porous body such as a sintered

body of fibers or particles or a foamed molded body.

Examples of the material included in the diffusion layer 10b

include a carbon woven fabric (carbon cloth), a carbon

nonwoven fabric, and carbon paper. Note that the diffusion

layer 10b may be omitted.

[0018] The anode electrode 12 oxidizes the hydroxide

ions so as to produce oxygen. The anode electrode 12 has a

metal such as iridium (Ir), ruthenium (Ru), platinum (Pt),

iron (Fe), cobalt (Co), nickel (Ni), and an oxide thereof, a

carbon material such as graphene, and a partial oxide thereof as an anode catalyst for oxidizing hydroxide ions. The anode catalyst may be dispersedly supported or coated on a base material having electron conductivity. The base material includes a material containing, for example, a metal such as titanium (Ti) or stainless steel (SUS) as a main component.

Examples of the form of the base material include a woven

fabric sheet or a nonwoven fabric sheet, a mesh, a porous

sintered body, a foamed molded body (foam), and an expanded

metal.

[0019] The electrolyte membrane 14 is disposed between

the cathode electrode 10 and the anode electrode 12. The

electrolyte membrane 14 is composed of an anion exchange

membrane and moves hydroxide ions from the cathode electrode

10 side to the anode electrode 12 side. Examples of the

anion exchange membrane that can be used for the electrolyte

membrane 14 include a known anion exchange membrane such as

Fumasep (registered trademark) (manufactured by FuMA-Tech).

Further, the electrolyte membrane 14 is more preferably

composed of a polymer having a main chain resistant to the

substance to be hydrogenated. Examples of such a polymer

include a polymer having an aromatic ring in the main chain

skeleton, such as a polyarylene. Since the electrolyte

membrane 14 has a rigid skeleton such as polyarylene,

resistance to the substance to be hydrogenated can be

increased. Thereby, cross-leakage of the substance to be

hydrogenated to the anode electrode side can be further suppressed.

[0020] The plate member 16a and the plate member 16b are

made of a metal such as stainless steel or titanium, for

example. The plate member 16a is stacked on the membrane

electrode assembly 8 from the side of the cathode electrode

10. The plate member 16b is stacked on the membrane

electrode assembly 8 from the side of the anode electrode 12.

Accordingly, the membrane electrode assembly 8 is sandwiched

between the pair of plate members 16a and 16b. A gap between

the plate member 16a and the membrane electrode assembly 8 is

sealed with the gasket 18a. A gap between the plate member

16b and the membrane electrode assembly 8 is sealed with the

gasket 18b. When the organic hydride production system 1

includes only one organic hydride production apparatus 2, the

pair of plate members 16a and 16b can correspond to so-called

end plates. When the organic hydride production system 1

includes a plurality of apparatuses 2 for producing an

organic hydride, and another apparatus 2 for producing an

organic hydride is arranged next to the plate member 16a or

the plate member 16b, the plate member can correspond to a

so-called separator.

[0021] The cathode flow path 20 is connected to the

cathode electrode 10. The cathode flow path 20 feeds and

discharges a catholyte LC to and from the cathode electrode

10. A groove may be provided on a main surface facing the

cathode electrode 10 side in the plate member 16a, and this groove may constitute the cathode flow path 20.

[0022] The anode flow path 22 is connected to the anode

electrode 12. The anode flow path 22 feeds and discharges an

anolyte LA to and from the anode electrode 12. A groove may

be provided on a main surface facing the anode electrode 12

side in the plate member 16b, and this groove may constitute

the anode flow path 22.

[0023] The catholyte LC is supplied to the cathode

electrode 10 by the catholyte supply device 4. The catholyte

supply device 4 has a catholyte tank 24, a first cathode pipe

26, a second cathode pipe 28, and a cathode pump 30. The

catholyte LC is stored in the catholyte tank 24. The

catholyte LC contains an organic hydride raw material, i.e.,

the substance to be hydrogenated. As an example, the

catholyte LC does not contain an organic hydride before the

start of the operation of the organic hydride production

system 1, and after the start of the operation, the organic

hydride generated by electrolysis is mixed in, whereby the

catholyte becomes the liquid mixture of the substance to be

hydrogenated and the organic hydride. The substance to be

hydrogenated and the organic hydride are preferably a liquid

at 200C and 1 atm.

[0024] The substance to be hydrogenated and the organic

hydride are not particularly limited as long as they are

organic compounds capable of adding/desorbing hydrogen by

reversibly causing a hydrogenation reaction/dehydrogenation reaction. As the substance to be hydrogenated and the organic hydride used in the present embodiment, an acetone isopropanol type, a benzoquinone-hydroquinone type, an aromatic hydrocarbon type, and the like can be widely used.

Among these, the aromatic hydrocarbon type is preferable from

the viewpoint of transportability during energy transport or

the like. In general, aromatic hydrocarbon-based substances

to be hydrogenated and organic hydrides are hydrophobic and

phase-separate from water at 200C and 1 atm.

[0025] An aromatic hydrocarbon compound used as the

substance to be hydrogenated is a compound containing at

least one aromatic ring. Examples of the aromatic

hydrocarbon compound include benzene, alkylbenzene,

naphthalene, alkylnaphthalene, anthracene, diphenylethane,

tetralin, and the like. The alkylbenzene contains a compound

in which 1 to 4 hydrogen atoms in the aromatic ring are

substituted with a linear alkyl group or a branched alkyl

group having 1 to 6 carbons. Examples of such a compound

include toluene, xylene, mesitylene, ethylbenzene, and

diethylbenzene. The alkylnaphthalene contains a compound in

which 1 to 4 hydrogen atoms in the aromatic ring are

substituted with a linear alkyl group or a branched alkyl

group having 1 to 6 carbons. Examples of such a compound

include methylnaphthalene. These compounds may be used alone

or in combination.

[0026] The substance to be hydrogenated is preferably at least one of toluene and benzene. It is also possible to use a nitrogen-containing heterocyclic aromatic compound such as quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, or N alkyldibenzopyrrole as the substance to be hydrogenated. The organic hydride is obtained by hydrogenating the above described substance to be hydrogenated, and examples thereof include cyclohexane, methylcyclohexane, dimethylcyclohexane, and decahydroquinoline.

[0027] The catholyte tank 24 is connected to the cathode

electrode 10 by the first cathode pipe 26. One end of the

first cathode pipe 26 is connected to the catholyte tank 24,

and the other end of the first cathode pipe 26 is connected

to the entrance of the cathode flow path 20. The cathode

pump 30 is provided in the middle of the first cathode pipe

26. The cathode pump 30 can be constituted by a known pump

such as a gear pump or a cylinder pump, for example. Note

that the catholyte supply device 4 may circulate the

catholyte LC using a liquid feeding device other than the

pump. The catholyte tank 24 is connected to the cathode

electrode 10 also by the second cathode pipe 28. One end of

the second cathode pipe 28 is connected to the exit of the

cathode flow path 20, and the other end of the second cathode

pipe 28 is connected to the catholyte tank 24.

[0028] The catholyte LC in the catholyte tank 24 flows

into the cathode electrode 10 through the first cathode pipe

26 by driving of the cathode pump 30. The catholyte LC flowing into the cathode electrode 10 is subjected to an electrode reaction in the cathode electrode 10. The catholyte LC in the cathode electrode 10 is returned to the catholyte tank 24 through the second cathode pipe 28. As an example, the catholyte tank 24 also functions as a gas-liquid separator. The hydrogen gas may be generated by the side reaction in the cathode electrode 10. Therefore, the hydrogen gas may be mixed in the catholyte LC discharged from the cathode electrode 10. The catholyte tank 24 separates the hydrogen gas in the catholyte LC from the catholyte LC and discharges the hydrogen gas to the outside of the system.

[0029] The electrolyte membrane 14 according to the

present embodiment is composed of an anion exchange membrane.

Thereby, as will be described in detail later, the movement

of an excessive amount of water from the anode electrode 12

to the cathode electrode 10 is suppressed. Therefore,

theoretically, the mixing of water into the catholyte LC can

be suppressed to a negligible extent. However, the catholyte

supply device 4 may be provided with an oil-water separator

for separating water from the catholyte LC as necessary.

Alternatively, the catholyte tank 24 may function as an oil

water separator.

[0030] In the catholyte supply device 4 according to the

present embodiment, the catholyte LC is circulated between

the cathode electrode 10 and the catholyte tank 24. However,

the present invention is not limited to this configuration, and the catholyte LC may be sent to the outside of the system from the cathode electrode 10 without being returned to the catholyte tank 24.

[0031] The anolyte LA is supplied to the anode electrode

12 by the anolyte supply device 6. The anolyte supply device

6 has an anolyte tank 32, a first anode pipe 34, a second

anode pipe 36, and an anode pump 38. The anolyte LA is

stored in the anolyte tank 32. The anolyte LA contains

water. Examples of the anolyte LA include an alkaline

solution such as: an aqueous solution of potassium hydroxide;

ion-exchanged water; and an aqueous solution containing an

inorganic electrolyte such as potassium sulfate.

[0032] The anolyte tank 32 is connected to the anode

electrode 12 by the first anode pipe 34. One end of the

first anode pipe 34 is connected to the anolyte tank 32, and

the other end of the first anode pipe 34 is connected to the

entrance of the anode flow path 22. The anode pump 38 is

provided in the middle of the first anode pipe 34. The anode

pump 38 can be constituted by a known pump such as a gear

pump or a cylinder pump, for example. Note that the anolyte

supply device 6 may circulate the anolyte LA using a liquid

feeding device other than the pump. The anolyte tank 32 is

connected to the anode electrode 12 by the second anode pipe

36. One end of the second anode pipe 36 is connected to the

exit of the anode flow path 22, and the other end of the

second anode pipe 36 is connected to the anolyte tank 32.

[00331 The anolyte LA in the anolyte tank 32 flows into

the anode electrode 12 through the first anode pipe 34 by

driving of the anode pump 38. A part of the water in the

anolyte LA flowing into the anode electrode 12 diffuses to

the cathode electrode 10 side via the electrolyte membrane 14

and is subjected to the electrode reaction at the cathode

electrode 10. The anolyte LA in the anode electrode 12 is

returned to the anolyte tank 32 through the second anode pipe

36. As an example, the anolyte tank 32 also functions as a

gas-liquid separator. In the anode electrode 12, oxygen gas

is generated by the electrode reaction. Therefore, the

oxygen gas is mixed into the anolyte LA discharged from the

anode electrode 12. The anolyte tank 32 separates the oxygen

gas in the anolyte LA from the anolyte LA and discharges the

oxygen gas to the outside of the system.

[0034] In the anolyte supply device 6 according to the

present embodiment, the anolyte LA is circulated between the

anode electrode 12 and the anolyte tank 32. However, the

present invention is not limited to this configuration, and

the anolyte LA may be sent from the anode electrode 12 to the

outside of the system without being returned to the anolyte

tank 32.

[00351 The apparatus 2 for producing an organic hydride

is supplied with power from an external power supply (not

shown). When power is supplied from the power supply to the

apparatus 2 for producing an organic hydride, a predetermined cell voltage is applied between the cathode electrode 10 and the anode electrode 12 of the apparatus 2 for producing an organic hydride, and an electrolytic current flows. The power supply sends power supplied from a power supply device to the apparatus 2 for producing an organic hydride. The power supply device can be constituted by a power generation device that generates power using renewable energy, for example, a wind power generation device, a solar power generation device, or the like. Note that the power supply device is not limited to such a renewable energy power generation device, and may be a system power supply, a storage device storing power from the power generation device using renewable energy or the system power supply, or the like. A combination of two or more of these devices may be used. Further, the configuration of the organic hydride production system 1 is not limited to those described above, and the configuration of each part can be appropriately changed.

[00361 A reaction that occurs in a case where toluene

(TL) is used as an example of the substance to be

hydrogenated in the organic hydride production apparatus 2 is

as follows. The organic hydride obtained in a case where

toluene is used as the substance to be hydrogenated is

methylcyclohexane (MCH).

<Electrode Reaction in Cathode Electrode>

TL + 6H 2 0 + 6e- - MCH + 60H-

<Electrode Reaction in Anode Electrode>

60H- - 3/202 + 3H 2 0 + 6e

[0037] That is, the electrode reaction in the cathode

electrode 10 and the electrode reaction in the anode

electrode 12 proceed in parallel. At the cathode electrode

10, toluene is hydrogenated with water so as to produce

methylcyclohexane and hydroxide ions. The hydroxide ions

generated at the cathode electrode 10 pass through the

electrolyte membrane 14 and move to the anode electrode 12.

The hydroxide ions supplied to the anode electrode 12 are

oxidized at the anode electrode 12 so as to generate oxygen,

water, and electrons. The electrons generated by the

oxidation of the hydroxide ions are supplied to the cathode

electrode 10 via an external circuit and are used for

electrode reaction at the cathode electrode 10.

[0038] Therefore, according to the apparatus 2 for

producing an organic hydride according to the present

embodiment, the oxidation reaction of the hydroxide ions and

the hydrogenation reaction of the substance to be

hydrogenated can be performed in one step. For this reason,

organic hydride production efficiency can be increased as

compared with a conventional technique in which the organic

hydride is produced by a two-step process which includes a

process of producing hydrogen by water electrolysis or the

like and a process of chemically hydrogenating the substance

to be hydrogenated in a reactor such as a plant.

Furthermore, since the reactor for performing the chemical

hydrogenation and a high-pressure vessel for storing the

hydrogen produced by the water electrolysis or the like are

not required, a significant reduction in facility cost can be

achieved.

[00391 Further, the apparatus 2 for producing an organic

hydride according to the present embodiment is an anion

exchange membrane (AEM) type, and moves hydroxide ions from

the cathode electrode 10 to the anode electrode 12.

Therefore, the direction of ion movement is opposite to that

of the conventional proton exchange membrane (PEM) type

apparatus. In this case, the movement of water from the

anode electrode 12 side to the cathode electrode 10 side is

theoretically only diffusion by the concentration gradient of

water. Hereinafter, water that moves from one electrode side

to the other electrode side due to the water concentration

gradient is referred to as "physical diffusion water" as

appropriate. In the case of the AEM type, the water

concentration of the anode is higher than that of the

cathode. Therefore, the physical diffusion water moves from

the anode electrode 12 side to the cathode electrode 10 side.

In the AEM type, the flow of electroosmotic water is in the

direction from the cathode electrode 10 side to the anode

electrode 12 side. Therefore, the water moving from the

anode electrode 12 side to the cathode electrode 10 side does

not contain electroosmotic water and contains only physical diffusion water. For this reason, the entry of an excessive amount of water into the cathode electrode 10 can be suppressed, and the inhibition of the diffusion of the substance to be hydrogenated due to the water in the cathode electrode 10 can be suppressed. Note that although the water originally held by the electrolyte membrane 14 can also enter the cathode electrode 10 as part of the physical diffusion water, the amount of this water is also a small amount compared to the amount of electroosmotic water in the PEM type device.

[0040] This allows the substance to be hydrogenated to

reach the reaction field easily. Therefore, the shortage of

the substance to be hydrogenated can be avoided, and the

occurrence of side reactions can be suppressed. Therefore,

the efficiency of the electrode reaction at the cathode

electrode 10, that is, a decrease in Faraday efficiency, can

be suppressed. In particular, it is possible to suppress a

decrease in reaction efficiency when a catholyte with a low

concentration of the substance to be hydrogenated is supplied

to the cathode electrode 10. As a result, the production

efficiency of the organic hydride is improved. Further,

since the accumulation of water in the cathode electrode 10

can be suppressed, the process of separating the organic

hydride and water from each other becomes easier or can be

omitted. In this respect, the production efficiency of

organic hydride is also improved.

[0041] In the case of the PEM type, water locally

disappears near the interface between the anode catalyst

layer and the electrolyte membrane due to the electrode

reaction at the anode electrode. On the other hand, a large

amount of electroosmotic water exists near the interface

between the cathode catalyst layer and the electrolyte

membrane. Therefore, the water on the cathode electrode side

can return to the anode electrode side due to the

concentration gradient of water. For this reason, the

direction of movement of the physical diffusion water is

opposite to that of the AEM type. Further, when the anolyte

LA is, for example, a solution containing a supporting

electrolyte, water can return from the cathode electrode side

to the anode electrode side due to the osmotic pressure

caused by the concentration gradient of the electrolyte.

Hereinafter, water that moves from one electrode side to the

other electrode side due to the electrolyte concentration

gradient is referred to as "osmotic pressure transfer water"

as appropriate. In the case of the PEM type, the osmotic

pressure transfer water moves from the cathode electrode 10

side to the anode electrode 12 side.

[0042] Therefore, in the PEM type, the physical

diffusion water and the osmotic pressure transfer water move

from the cathode electrode side to the anode electrode side.

Hereinafter, the water moving from the cathode electrode side

to the anode electrode side (physical diffusion water + osmotic pressure transfer water) in the PEM type is referred to as "back-diffusion water" as appropriate. "Back" in

"back-diffusion water" means that the direction is opposite

to the direction of ion movement. Further, the phenomenon

where the back-diffusion water returns to the anode electrode

side that occurs in the PEM type is called "back diffusion of

water."

[0043] When back diffusion of water occurs, a small

amount of the substance to be hydrogenated dissolved in the

water can also move to the anode electrode side along with

the water. As a result of this, the anode catalyst can be

deactivated by the substance to be hydrogenated. On the

other hand, since the accumulation of water in the cathode

electrode 10 is suppressed in the present embodiment, the

movement of water from the cathode electrode 10 side to the

anode electrode 12 side is also suppressed. Therefore, it is

possible to suppress the deactivation of the anode catalyst

by the substance to be hydrogenated. Further, the loss of

the substance to be hydrogenated from the cathode electrode

10 can also be suppressed. As a result, the production

efficiency of the organic hydride is improved.

[0044] In the case of the PEM type, the reaction

proceeds by the movement of protons from the anolyte to the

cathode electrode side in the state of oxonium ions.

Therefore, it is necessary to secure a proton (oxonium ion)

conduction path in the anolyte. Therefore, from the viewpoint of reaction promotion, proton activity, and the like, the anolyte is preferably neutral to acidic. Further, from the viewpoint of efficient proton conduction, the anode catalyst and the cathode catalyst are preferably coated with strongly acidic proton exchange ionomers. Therefore, the anode catalyst and the cathode catalyst are placed in an acidic atmosphere. For this reason, each catalyst is limited to what can be used in an acidic atmosphere. In particular, the anode catalyst is limited to materials that are resistant to acidic and oxidizing atmospheres.

[0045] On the other hand, hydroxide ions move from the

cathode electrode 10 side to the anode electrode 12 side in

the present embodiment. For this reason, the anolyte is

preferably neutral to alkaline. Further, from the viewpoint

of efficient hydroxide ion conduction, the anode catalyst and

cathode catalyst are preferably coated with alkaline anion

exchange ionomers. Therefore, the anode catalyst and the

cathode catalyst are placed in a neutral to alkaline

atmosphere. For this reason, each catalyst may be usable in

a neutral to alkaline atmosphere. There are more options for

the anode catalyst that can be used in a neutral to alkaline

atmosphere than in an acidic atmosphere. Therefore,

according to the present embodiment, the degree of design

freedom of the apparatus 2 for producing an organic hydride

can be increased, making it easy to reduce the cost of the

members and the like.

[0046] The lower the solubility of the substance to be

hydrogenated and the organic hydride in water is, the more

effective it is to suppress the movement of water from the

anode electrode 12 side to the cathode electrode 10 side.

For example, the suppression of water movement is more

effective when the solubility in water at 250C of at least

one of the substance to be hydrogenated and the organic

hydride is preferably 3 g/100 mL or less and more preferably

2 g/100 mL or less. The removal of water by the substance to

be hydrogenated and the organic hydride becomes significantly

difficult when the solubility in water of at least one of the

substance to be hydrogenated and the organic hydride is 3

g/100 mL or less. Therefore, the suppression of water

movement is more effective. Examples of the substance to be

hydrogenated and the organic hydride that are particularly

expected to have this effect include benzene (0.18 g/100 mL

H 2 0) and cyclohexane (0.36 g/100 mL H 2 0), toluene (0.05 g/100

mL H 2 0) and methylcyclohexane (1.6 g/100 mL H 2 0), naphthalene

(0.003 g/100 mL H 2 0) and decahydronaphthalene (0.001 g/100 mL

H 2 0), and the like.

[0047] The water used for the electrode reaction at the

cathode electrode 10 is preferably provided from physical

diffusion water entering from the electrolyte membrane 14.

The physical diffusion water includes at least one of the

water derived from the anolyte LA and the water originally

held by the electrolyte membrane 14. That is, the water in the anolyte LA diffuses from the anode electrode 12 side to the cathode electrode 10 side via the electrolyte membrane 14 due to the concentration gradient of water. Further, the electrolyte membrane 14 may absorb and retain water in the atmosphere. Alternatively, the electrolyte membrane 14 can be subjected to a water impregnation treatment when assembling the apparatus 2 for producing an organic hydride.

This water can also enter the cathode electrode 10 side due

to the concentration gradient of water.

[0048] The amount of water entering from the electrolyte

membrane 14 to the cathode electrode 10 side is preferably

adjusted to an amount necessary and sufficient for

hydrogenating the substance to be hydrogenated at the cathode

electrode 10 and not inhibiting the substance to be

hydrogenated from reaching the reaction field. If the amount

of water entering the cathode electrode 10 side is

insufficient, not only will there be a shortage of water as a

substrate, but the ionomers in the cathode catalyst layer

will not be wetted, making it difficult to form ion

conduction paths between the ion exchange groups. Therefore,

the hydrogenation of the substance to be hydrogenated can be

inhibited. Conversely, if the amount of water entering the

cathode electrode 10 side becomes excessive, the arrival of

the substance to be hydrogenated to the reaction field can be

inhibited. As a result, hydrogen generation due to a side

reaction can become dominant at the cathode electrode 10.

The amount of water is determined by the physical diffusion

water and the osmotic transfer water that are via the

electrolyte membrane 14. Therefore, the amount of water can

be controlled by the material and film thickness of the

electrolyte membrane 14, the operating temperature of the

apparatus 2 for producing an organic hydride, the support

electrolyte concentration of the anolyte, and the like. The

amount of water can be defined, for example, by a unit time

during non-electrolysis and the amount of water per area of

the electrolyte membrane 14 (mg/min/m2 ). Further, the

appropriate range of the amount of water is preferably 1.05

to 1.70/min, for example, when expressed as the ratio (/min)

of the physical amount of water per unit time during non

electrolysis and area of the electrolyte membrane 14 to the

number of ion exchange groups (mmol/m 2 ) per area of the

ionomers in the cathode catalyst layer. By setting the

amount of water to 1.05/min or more, it is possible to more

reliably suppress a decrease in the performance of the

apparatus 2 for producing an organic hydride due to

inhibition of hydrogenation caused by a lack of water.

Further, by setting the amount of water to 1.70/min or less,

it is possible to more reliably suppress the inhibition of

the reaction due to the accumulation of excess water in the

cathode catalyst layer.

[0049] The cathode electrode 10 uses at least one of

water derived from the anolyte LA and water derived from the electrolyte membrane 14 that has entered the cathode electrode 10 from the electrolyte membrane 14 for a reaction with the substance to be hydrogenated. Thereby, compared to the case where water is directly supplied to the cathode electrode 10 from the outside of the apparatus 2 for producing an organic hydride, it is easier to suppress the inhibition of the diffusion of the substance to be hydrogenated due to water, the complication of the recovery process of the organic hydride, the occurrence of back diffusion of water, and the like. Although the water used in the cathode electrode 10 is preferably only water entering from the electrolyte membrane 14, direct water absorption from the outside into the cathode electrode 10 may be appropriately combined.

[00501 The embodiments may be defined by the items

described in the following.

[Item 1]

An apparatus (2) for producing an organic hydride

including:

a cathode electrode (10) that generates an organic

hydride and hydroxide ions from a subject to be hydrogenated

and water;

an anode electrode (12) that produces oxygen by

oxidizing the hydroxide ions; and

an electrolyte membrane (14) that is composed of an

anion exchange membrane and is arranged between the cathode electrode (10) and the anode electrode (12) so as to transfer the hydroxide ions from the cathode electrode (10) side to the anode electrode (12) side.

[Item 2]

The apparatus (2) for producing an organic hydride

according to Item 1, wherein

the anode electrode (12) is supplied with an anolyte

(LA) containing water,

the electrolyte membrane (14) contains water, and

the cathode electrode (10) uses water entering from the

electrolyte membrane (14) for a reaction with the substance

to be hydrogenated.

[Item 3]

A method for producing an organic hydride in which the

apparatus (2) for producing an organic hydride according to

Item 1 or 2 is used, including:

producing an organic hydride and hydroxide ions from

the substance to be hydrogenated and water at the cathode

electrode (10);

moving the hydroxide ions to the anode electrode (12)

via the electrolyte membrane (14); and

producing oxygen by oxidizing the hydroxide ions at the

anode electrode (12).

Exemplary Embodiments

[0051] Hereinafter, exemplary embodiments of the present

invention will be explained. However, these exemplary embodiments are merely examples for suitably explaining the present invention and do not limit the present invention in any way.

(First Exemplary Embodiment)

[0052] A quaternary ammonium-based AEM-type electrolyte

membrane (Fumasep (registered trademark) FAA-3-PK-130,

manufactured by FuMA-Tech) having a polyarylene skeleton was

prepared. The thickness of this electrolyte membrane was 130

pm. The degree of water permeability during non-electrolysis

in the electrolyte membrane was measured according to the

following procedure.

[0053] That is, the electrolyte membrane was cut out

into a circle having p of 40 mm. An electrolyte membrane

sandwiched between circular Viton (registered trademark)

gaskets was fixed between two flange glass cells of an H-type

cell (VB9B, manufactured by EC FRONTIER CO., LTD). The

exposed portion of the electrolyte membrane had T of 28 mm.

The flange glass cell on one side was filled with 25 mL of 1

mol/L KOH aqueous solution. The weight of the entire H-type

cell was measured, and the measured weight was set as a

starting weight (Amg). The openings of the flange glass

cells on the respective sides were sealed with parafilms and

left to stand. After a predetermined time, the parafilms

sealing the openings were removed, and the water diffused

into the flange glass cell on the side not filled with the

KOH solution was wiped off. The weight of the entire H-type cell was measured again, and the measured weight was set as an ending weight (Bmg). Then, based on the following equation (1), the permeability of water during non electrolysis was calculated.

Equation (1): (A-B) [mg]/standing time [min]/area of

exposed part of electrolyte membrane [m 2 ]

[0054] An anode catalyst ink was prepared by mixing an

IrO2 catalyst (manufactured by Furuya Metal Co.,Ltd.), a

quaternary ammonium-based anion-exchange ionomer (Fumion

(registered trademark) FAA-3-SOLUT-10, manufactured by FuMA

Tech), pure water, and 1-propanol (manufactured by FUJIFILM

Wako Pure Chemical Corporation). The catalyst support

density of the anode catalyst ink was 1.5 mg/cm 2 , and the

ionomer/catalyst ratio (I/Cat) was 0.1. An anode catalyst

layer was formed by applying a prepared anode catalyst ink to

one of the main surfaces of the above-described AEM-type

electrolyte membrane.

[00551 A cathode catalyst ink was prepared by mixing

PtRu / C catalyst (TEC61E54, manufactured by TANAKA PRECIOUS

METAL TECHNOLOGIES Co., Ltd.), a quaternary ammonium-based

anion-exchange ionomer (Fumion (registered trademark) FAA-3

SOLUT-10, manufactured by FuMA-Tech), pure water, and 1

propanol (manufactured by FUJIFILM Wako Pure Chemical

Corporation). The catalyst support density of the cathode

catalyst ink was 1 mg/cm 2 , and the ionomer/carbon ratio (I/C)

was 0.8. A cathode catalyst layer was formed by applying a prepared cathode catalyst ink to the opposite main surface of the AEM-type electrolyte membrane in which an anode catalyst layer was formed on one main surface. Based on the composition of the cathode catalyst ink, the permeated water amount ratio to the ion exchange group amount of the ionomers was calculated using the following equation (2). The ion exchange capacity (IEC) of the quaternary ammonium-based anion-exchange ionomer used in the present exemplary embodiment was 1.86 mmol/g.

Equation (2): (water permeability during non

electrolysis [mg/min/m 2 ]/molecular weight of water

[g/mol])/(ionomer content in catalyst layer [mg/m2 ] x ionomer

ion exchange capacity [mmol/g])

[00561 The apparatus for producing an organic hydride

according to the first exemplary embodiment was obtained by

stacking a cathode end plate, a cathode side gasket, a

diffusion layer, an AEM-type electrolyte membrane having a

cathode catalyst layer and an anode catalyst layer stacked

thereon, an anode side gasket, and an anode end plate in the

order stated. For each end plate, a titanium plate with a

flow path for each solution was used. Each gasket was

manufactured by Viton (registered trademark). The electrode

effective area of the apparatus for producing an organic

hydride was 25 cm 2 .

[0057] Toluene serving as a catholyte was circulated to

the cathode of the apparatus for producing an organic hydride at a flow rate of 20 mL/min. Further, a 1 mol/L KOH aqueous solution serving as an anolyte was circulated at the anode at a flow rate of 20 mL/min. Then, an electrolytic reaction was performed at a temperature of 600C and a predetermined cell voltage. The Faraday efficiency was calculated from the amount of electricity consumed by the electrolytic reaction and the amount of organic hydride generated. Then, the

Faraday efficiency of 80% or more is evaluated as 0, and the

Faraday efficiency of less than 80% is evaluated as x.

Further, after the electrolytic reaction, the amount of water

in the catholyte was measured by separating and weighing the

aqueous layer in a catholyte container. Then, a ratio of

water mixed in the entire catholyte after electrolysis of

less than 1% was evaluated as 0, and a ratio of water mixed

in the entire catholyte after electrolysis of 1% or more was

evaluated as x. The results are shown in Fig. 2.

(Second Exemplary Embodiment)

[00581 The water permeability measurement, the

preparation of an apparatus for producing an organic hydride,

the electrolysis treatment, the calculation of the permeated

water amount ratio, and each evaluation were carried out in

the same manner as in the first exemplary embodiment, except

that ion-exchanged water was used for the water permeability

measurement and the anolyte. The results are shown in Fig.

2.

(First Comparative Example)

[00591 A polyfluorosulfonic acid-based PEM-type

electrolyte membrane (Nafion (registered trademark) 117,

manufactured by The Chemours Company) was prepared. The

thickness of this electrolyte membrane was 180 pm. The

degree of water permeability in this electrolyte membrane was

measured in the same manner as in the second exemplary

embodiment.

[00601 An anode catalyst ink was prepared by mixing an

IrO2 catalyst (manufactured by Furuya Metal Co., Ltd.), a

polyfluorosulfonic acid cation-exchange ionomer (Nafion

(registered trademark) DE2020CS, manufactured by The Chemours

Company), ion-exchanged water, and 1-propanol (manufactured

by FUJIFILM Wako Pure Chemical Corporation). The catalyst

support density of the anode catalyst ink was 1.5 mg/cm 2, and

the ionomer/catalyst ratio (I/Cat) was 0.1. An anode

catalyst layer was formed by applying a prepared anode

catalyst ink to one of the main surfaces of the above

described PEM-type electrolyte membrane.

[00611 A cathode catalyst ink was prepared by mixing a

PtRu/C catalyst (TEC61E54, manufactured by TANAKA PRECIOUS

METAL TECHNOLOGIES Co., Ltd.), a polyfluorosulfonic acid

based cation-exchanged ionomer (Nafion (registered trademark)

DE2020CS, manufactured by The Chemours Company), ion

exchanged water, and 1-propanol (manufactured by FUJIFILM

Wako Pure Chemical Corporation). The catalyst support

density of the cathode catalyst ink was 1 mg/cm 2 , and the ionomer/carbon ratio (I/C) was 0.5. A cathode catalyst layer was formed by applying a prepared cathode catalyst ink to the opposite main surface of the PEM-type electrolyte membrane in which an anode catalyst layer was formed on one main surface.

Based on the composition of the cathode catalyst ink, the

permeated water amount ratio to the ion exchange group amount

of the ionomers was calculated in the same way as in the

first and second exemplary embodiments. The ion exchange

capacity of the polyfluorosulfonic acid cation-exchange

ionomer used in the present comparative example was 1.00

mmol/g.

[0062] The apparatus for producing an organic hydride

according to the first comparative example was obtained by

stacking a cathode end plate, a cathode side gasket, a

diffusion layer, a PEM-type electrolyte membrane having a

cathode catalyst layer and an anode catalyst layer stacked

thereon, an anode side gasket, and an anode end plate in the

order stated. Each end plate and each spacer were the same

as those used in the first exemplary embodiment. The

electrode effective area of the apparatus for producing an

organic hydride was 25 cm 2 . Using the obtained apparatus for

producing an organic hydride, electrolytic treatment and each

evaluation were performed in the same manner as in the second

exemplary embodiment. The results are shown in Fig. 2.

[0063] Fig. 2 is a diagram showing evaluation results of

the Faraday efficiency and evaluation results of water mixed into a catholyte in each of exemplary embodiments and comparative examples. From the comparison between the first and second exemplary embodiments and the first comparative example, it has been confirmed that when the apparatus for producing an organic hydride includes an AEM type electrolyte membrane, the ratio of water mixed in the catholyte after electrolysis is less than 1%, which is an extremely small amount, and a Faraday efficiency of 80% or more can be obtained at least at any of the cell voltages. Therefore, it has been confirmed that the use of an AEM-type electrolyte membrane can improve the production efficiency of an organic hydride.

[0064] Further, from the comparison between the first

and second exemplary embodiments, it has been confirmed that

a Faraday efficiency of 80% or more can be obtained at a

wider range of cell voltages when the anolyte does not

contain a support electrolyte than when the anolyte contains

a support electrolyte. Further, it has been confirmed that

the degree of water permeability during non-electrolysis and

a permeated water amount ratio to the ionomer ion exchange

group amount are higher in the second exemplary embodiment

than those in the first exemplary embodiment. From this, by

reducing the support electrolyte concentration of the

anolyte, it has been shown that the physical diffusion water

moved from the anode electrode 12 side to the cathode

electrode 10 side can be suppressed from returning to the anode electrode 12 side as osmotic pressure transfer water due to the concentration gradient of the support electrolyte.

Thereby, more water can be supplied to the cathode electrode

10 side. Therefore, it is possible to prevent the supply of

water to the cathode electrode 10 from becoming the rate

limiting factor for the cathode reaction. Therefore, the

cell voltage can be increased to increase the current density

of the electrolytic reaction, in other words, the reaction

rate. In all of the first and second exemplary embodiments

and the first comparative example, cross leakage of toluene

to the anode electrode side was not observed.

INDUSTRIAL APPLICABILITY

[00651 The present invention can be used for an

apparatus for producing an organic hydride and a method for

producing an organic hydride.

REFERENCE SIGNS LIST

[00661 2 apparatus for producing an organic hydride, 10

cathode electrode, 12 anode electrode, 14 electrolyte

membrane, LA anolyte, LC catholyte

Claims (3)

1. [Claim 1]

   An apparatus for producing an organic hydride

   comprising:

   a cathode electrode that generates an organic hydride

   and hydroxide ions from a subject to be hydrogenated and

   water;

   an anode electrode that produces oxygen by oxidizing

   the hydroxide ions; and

   an electrolyte membrane that is composed of an anion

   exchange membrane and is arranged between the cathode

   electrode and the anode electrode so as to transfer the

   hydroxide ions from the cathode electrode side to the anode

   electrode side.
2. [Claim 2]

   The apparatus for producing an organic hydride

   according to Claim 1, wherein

   the anode electrode is supplied with an anolyte

   containing water,

   the electrolyte membrane contains water, and

   the cathode electrode uses water entering from the

   electrolyte membrane for a reaction with the substance to be

   hydrogenated.
3. [Claim 3]

   A method for producing an organic hydride in which the

   apparatus for producing an organic hydride according to Claim

   1 or 2 is used, comprising:

   producing an organic hydride and hydroxide ions from

   the substance to be hydrogenated and water at the cathode

   electrode;

   moving the hydroxide ions to the anode electrode via

   the electrolyte membrane; and

   producing oxygen by oxidizing the hydroxide ions at the

   anode electrode.